Stromatolite ( ) or stromatoliths (from the Greek > ???? ? str? ma "layer, stratum" ( GEN ???? and ????? litos "rock") is a mound of layers, columns, and sedimentary rocks like sheets that were originally formed by the growth of layer by layer of cyanobacteria, one-celled photosynthetic microbes. Fossilized stromatolites, some of which may have come from 3.7 billion years ago, provide a record of ancient life on Earth. Lichen Stromatolite is a proposed mechanism for the formation of several types of layered rock structures formed on the water, where stones meet air, by repeated colonization of stones by endolitic moss.
Video Stromatolite
Morphology
Stromatolites are bio-chemical accretion accretion structures formed in shallow water by trapping, binding and cementation of sediment granules by biofilms (microbial mats) of microorganisms, especially cyanobacteria. They exhibit various shapes and structures, or morphologies, including conical, stratiform, branching, domal, and columnar types. Stromatolites occur widely in the Precambrian fossil record, but are rare today. Very few ancient stromatolites contain microbial fossils. While the features of some stromatolites are suggestive of biological activity, others have features that are more consistent with abiotic (non-biological) deposition. Finding a reliable way to distinguish between biologically-formed and abiotic stromatolites is an active area of ​​research in geology.
Maps Stromatolite
Formation
Time lapse photography from the formation of modern microbial mats in laboratory settings provides some clues that reveal the behavior of cyanobacteria in stromatolites. Biddanda et al. (2015) found that cyanobacteria exposed to local light rays move toward light, or express phototaxis, and increase their photosynthesis results, which are necessary for survival. In a new experiment, scientists project the school logo into petri dishes containing organisms, which grow below the bright areas, forming a logo on bacteria. The authors speculate that such motility allows the cyanobacteria to seek light sources to support the colony. In light and dark conditions, cyanobacteria form clumps that then expand outward, with remaining individual members connected to the colony through long tendrils. This may be a protection mechanism that provides an evolutionary benefit for colonies in harsh environments where mechanical forces act to tear the microbial mats. Thus this sometimes complex structure, built by microscopic organisms that work somewhat simultaneously, is a means of providing protection and protection from harsh environments.
Fossil record
Some Archean rock formations show macroscopic similarities to modern microbial structures, leading to the conclusion that these structures are evidence of ancient life, the stromatolites. Others, however, consider this pattern to be the result of deposition of a natural material or some other abiogenic mechanism. Scientists contend for the biological origin of stromatolites due to the presence of globular organic groups in the thin layer of stromatolites, of the aragonite nanocrystals (both features of the current stromatolites), and because of the persistence of biological signals concluded through changes in environmental circumstances..
Stromatolites are the main constituents of the fossil record of the first life forms on earth. The earliest known fossils, found in the suprasrustal belt of Isua in Southwest Greenland, came from 3.7 billion years ago. They peaked about 1.25 billion years ago and then declined in abundance and diversity, so that at the beginning of the Cambrian they had fallen to 20% of the peak. The most widely supported explanation is that the builders of stromatolites fall victim to grazing creatures (revolutions of the Cambrian substrate); this theory implies that a fairly complex organism was common more than 1 billion years ago.
Proterozoic stromatolite microphosphates (preserved by permineralization in silica) include cyanobacteria and possibly some form of eukaryotic chlorophyll (ie green algae). A very common genus of stromatolites in geological records is Collenia .
The relationship between grazer abundance and stromatolites is well documented in the younger Ordovician evolution radiation; The abundance of stromatolites also increased after the end-Ordovician and end Permian extinctions thinned marine animals, falling back to previous levels as marine animals recovered. Fluctuations in metazoa populations and diversity may not be the only factor in the reduction of stromatolite abundance. Factors such as environmental chemistry may be responsible for change.
While prokaryotic cyanobacteria reproduce asexually through cell division, they play a role in preparing the environment for the evolutionary development of more complex eukaryotic organisms. Cyanobacteria (as well as extremist Gammaproteobacteria) are thought to be very responsible for increasing the amount of oxygen in the primordial earth's atmosphere through their continuous photosynthesis (see Great Oxygenation Event). Cyanobacteria use water, carbon dioxide, and sunlight to create their food. The mucus layer is often formed on cyanobacterial cell mats. In modern microbial mats, debris from adjacent habitats can be trapped inside the mucus, which can be cemented together by calcium carbonate to grow thin lime laminates. These laminates can accumulate over time, resulting in a common ribbon pattern for stromatolites. Domogenic morphology of biological stromatolites is a result of the vertical growth necessary for infiltration of sunlight into organisms for photosynthesis. The structures of spherical growth called oncolites are similar to stromatolites and are also known from the fossil record. Thrombolite is a poor lamination or lamination clumping structure formed by cyanobacteria, common in modern fossil records and sediments.
The Zebra River Canyon area of ​​the highly cleaved Zaris River in the Zaris platform in southern Namibia provides an example of exposure to the thrombolite-stromatolite-metazoan reefs that developed during the Proterozoic period, stromatolites here develop better at the updip site under higher current velocity conditions and greater sediment inflows.
Modern events
Modern stromatolites are mostly found in hypersaline lakes and marine lagoons where extreme conditions because of high salt levels prevent animal grazing. One such location is the Hamelin Pool Nature Reserve, Shark Bay in Western Australia where excellent specimens are observed today, the Pampa del Tamarugal Nature Reserve in Chile and the other is Lagoa Salgada ("Salty Lake"), in the state of the Rio Grande do Norte, Brazil, where modern stromatolites can be observed as bioherm (domal type) and bed. Mainland stromatolites can also be found in marine waters in the Cuatro CiÃÆ'Â © negas, a unique ecosystem in the Mexican desert, and in Lake Alchichica, the lake maar in the Oriental Basin of Mexico. The only open ocean environment in which modern stromatolites are known to prosper is Exuma Cays in the Bahamas.
In 2010, the five types of Chlorophyll, Chlorophyll f, were discovered by Dr. Min Chen from stromatolites in Shark Bay.
Modern freshwater stromatolite
Bacalar Lagoon in YucatÃÆ'¡n The southern Peninsula of Mexico in the state of Quintana Roo, has a vast formation of giant living microbes (ie, stromatolites or thrombolites). The microbialite bed is over 10 km (6.2 miles) long with a few meters vertical rise in some areas. It may be the largest living freshwater microbial, or any organism, on Earth.
Slightly further south, a 1.5-km stretch of stromatolite that forms corals (especially of the Scytonema genus) occurs in Chetumal Bay in Belize, just south of Rio Hondo and Mexico's mouth.
Fresh water stromatolites are found on Lake Salda in southern Turkey. Waters are rich in magnesium and stromatolite structures made of hydromagnesite.
Another pair of examples of freshwater stromatolites exist in the Pavilion and Lake Kelly in British Columbia, Canada. Lake Pavilion has the largest freshwater stromatolite known and has been studied by NASA as part of xenobiology research. NASA, the Canadian Space Agency, and a number of universities from around the world are collaborating on projects that center on studying microbial life in lakes. Called the "Pavilion Lakes Research Project" (PLRP), the goal is to study what conditions exist in the bottom of the lake that are most likely to live lives and develop better hypotheses about how environmental factors affect microbial life. The ultimate goal of this project is to better understand what conditions will be more likely to live life on other planets. There is an online citizens science project called "MAPPER" where anyone can help sort through thousands of lake bottom photos and mark the microbes, algae and other lake features.
Microbes have been found in open pit ponds in an abandoned asbestos mine near Clinton Creek, Yukon, Canada. These microbes are very young and may begin to form soon after the mine closes in 1978. The combination of low sedimentation rates, high calcification rates, and low microbial growth rates seems to result in the formation of these microbes. Microbes in historic mine sites suggest that anthropogenically constructed environments may encourage microbial carbonate formation. It has implications for creating an artificial environment for building modern microbes including stromatolites.
A very rare type of strumolite lives in a non-lake lake in Nettle Cave in Jenolan Cave, NSW, Australia. Cyanobacteria live on the surface of limestone, and are sustained by calcium-rich water, allowing them to grow toward the two open ends of the cave that give light.
Source of the article : Wikipedia
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